1. Field of the Invention
The present invention relates to an apparatus and a method for detecting energy of a tone signal, and more particularly, to an apparatus and a method for detecting energy of a tone signal by using a nonlinear tracer. The present application is based on Korean Patent Application No. 2001-69657, filed Nov. 9, 2001, which is incorporated herein by reference.
2. Description of the Related Art
A burst detector has a very important role in a frame transmission system using a preamble. Basically, the burst detector performs a function of detecting the exact time that a frame transmitted to a receiver is received. A detection result of the burst detector generally can be used for two aspects in the receiver.
First of all, unnecessary signal processing and power consumption can be reduced by deciding an appropriate time for the operation of a synchronizer of the receiver. Most receivers define an operation mode and a stand-by mode to prevent power consumption due to unnecessary operation of the receiver when there are no incoming frames. The result of the burst detection is used to decide the mode of operation of the receiver.
Second, the synchronizer of the receiver of the system using a preamble can be operated by a data-aided (DA) method. The method uses a certain preamble pattern decided by the transmitter and receiver, and thus the exact receiving time of the frame is detected and a correlation between a received signal and the preamble is used for a synchronous algorithm.
Generally, burst detection is the same as a process of detecting energy of a signal. As a generally used energy detection algorithm, there are several methods using an absolute value detector (AVD), a root mean square detector (RMSD), and a square law detector (SLD). Energy detection is realized as an absolute value, a square root, and a square being accumulated for a predetermined interval.
While these methods can be used for adjusting the operation mode of the synchronizer, they are not suitable for use with a synchronizer operating according to the DA method since the probability of exactly detecting the burst start symbol detection is low. In other words, when there are many samples, it is hard to detect the exact position (tone element) of the first symbol of the burst. On the contrary, when there are few samples, the number of samples which can be used for observation is also scanty. Thus detection of the energy is unstable and the probability of burst detection success is lower as well. Accordingly, a tone energy detector is appropriate as a burst detector used for adjusting the operation mode of the synchronizer of the receiver and demodulating of the DA method.
Therefore, conventionally, a method using a teager energy operator (TEO) is usually used to detect the symbol of the exact receiving time of the burst. The TEO algorithm is used for detecting a tone signal element of a communication system or a system relating to electroencephalograms used in the medical field. The result of the burst detection by the TEO algorithm is input into the synchronizer of the receiver to decide the operation time and provides a synchronous environment in a receiver using the DA method.
FIG. 1 is a block diagram showing a structure of the apparatus for detecting the energy of the tone signal using a conventional TEO method. FIG. 2 is a view showing the principle of operation of the conventional TEO method.
Referring to FIGS. 1 and 2, the apparatus for detecting the energy of the tone signal using the conventional TEO method has a delay unit 100, a square multiplier 110, a multiplier 120, and a subtractor 130.
Delay unit 100 outputs a sample stream after delaying a transmitted sample stream by a unit of one sample. The square multiplier 110 squares a center sample, where the time the center sample is received is the reference time, for detecting the existence of the tone element, among three samples consecutively transmitted. The multiplier 120 outputs a value after multiplying samples before and after the center sample. The subtractor 130 subtracts a value input by the multiplier 120 from a value input by the square multiplier 110 and outputs the value resulting from the subtraction.
On the other hand, FIG. 2 shows an input and an output of each of the elements shown in FIG. 1. The sample stream input to the delay unit 100 consists of a series of samples obtained by taking one sample per symbol. A signal s(k) input into the square multiplier 110 is a sample transmitted kth, and signals input into the multiplier 120 are samples s(k−1) and s(k+1) that are before and after the signal s(k). Moreover, the output T[s(k)] of the subtractor 130, that is, the final value yielded by the TEO algorithm, is expressed by the following mathematical expression.T[s(k)]=s2(k)−s(k−1)s(k+1)  [Mathematical expression 1]
Here, s(k) is a sample transmitted kth, and T[s(k)] is an output of the TEO algorithm of the kth sample. The TEO algorithm can be performed from the mathematical expression 1 by using the transmitted sample. The total number of samples are three: a center sample of the time for detecting the existence of the tone element, and samples before and after the center sample.
Yet, the TEO algorithm has a high probability of providing a false alarm due to an impulse error and a burst error generated on a channel and has a low probability of success of the burst detection due to a signal attenuation generated at the kth sample for detecting the existence of the burst. Therefore, the TEO algorithm has a high probability of a frame error.